Abstract: Process for the preparation of pure, unsymmetrically disubstituted ureas of the general formula ##STR1## in which R denotes a phenyl radical which is unsubstituted, or monosubstituted or polysubstituted by halogen atoms or alkyl, alkoxy, aryloxy or trifluoromethyl groups, an oxazolyl, isoxazolyl, thiazolyl, isothiazolyl, benzoxazolyl or benzothiazolyl radical which is unsubstituted, or monosubstituted or polysubstituted by halogen atoms or alkyl, alkoxy or trifluoromethyl groups and R.sub.1 and R.sub.2 independently of one another denote a hydrogen atom or an alkyl group, where R.sub.1 and R.sub.2 are not simultaneously hydrogen or R.sub.1 and R.sub.2 together denote a butylene or pentylene group, by reaction of an N-alkyl- or N,N-dialkylurea with an unsubstituted or substituted arylamine or a heterocyclic amine in the presence of that amine which is already present in the starting material, the respective N-alkyl- or N,N-dialkylurea.